1. Field of the Invention
The present invention is generally related to a pressure control method and, more particularly, to a method for controlling fuel pressure at a fuel injector by controlling the operational speed of a fuel pump.
2. Description of the Prior Art
U.S. Pat. No. 6,357,422, which issued to Doane et al on Mar. 19, 2002, describes a fuel pressure regulation system for use in a fuel pump system in which atomizing air is injected into the fuel delivered to the injector. The system includes both an air rail and a fuel rail and is operable to maintain the fuel pressure within the system at a consistent pressure above the air rail pressure. The system also includes a first pressure sensor, a second pressure sensor, a control circuit, and a fuel pressure pump or other fuel control device. The first and second pressure sensors are differential pressure sensors which measure the air and fuel pressure, respectively, convert those measurements into first and second electronic signals, and send those signals to the control circuit. The control circuit is an electronic circuit that includes a first stage, a second stage, and an output stage and provides the fuel pump with a closed loop control based on the first and second signals. Preferably, the closed loop control is achieved using both proportional and integral control with the output being in the form of a pulse-width modulated signal. The fuel pump is in fluid communication with the fuel rail and adjusts the fluid pressure within the fuel rail according to the pulse-width signal sent by the control circuit.
U.S. Pat. No. 3,822,677, which issued to Reddy on Jul. 9, 1974, describes an electric fuel pump control circuit for intermittent injection electronic fuel control systems. The circuit provides optimum fuel delivery at constant operating pressure to the fuel injector valve means of an electronically controlled fuel supply system. By energizing the pump in response to the engine operating parameters which determine the fuel requirement, a minimum of fuel in excess of the fuel requirement is recirculated from the area of the engine back to the fuel reservoir. In order to suitably energize the fuel pump, the pump is provided with a maximum voltage during the time period of the injection pulse with the energization voltage decreasing thereafter so that a minimum of fuel is circulated through the fuel supply system during the noninjection phase. This provides a variable level of average fuel pump energization.
U.S. Pat. No. 4,982,331, which issued to Miyazaki on Jan. 1, 1991, describes a fuel injector control apparatus. The apparatus is intended for a fuel injector and has a microcomputer which calculates a basic pulse width of pulses to be applied to a fuel injector. When the voltage of a battery which powers a fuel pump and the fuel temperature fall below levels which cause the discharge pressure of the fuel pump to drop below a prescribed pressure, the microcomputer corrects the basic pulse width by lengthening it to compensate for the drop in fuel pressure. Pulses having the corrected pulse width are applied to the fuel injector.
U.S. Pat. No. 6,516,784, which issued to Shingu on Feb. 11, 2003, describes a pressure accumulating distribution type of fuel injection pump. The pump is for a low pollution diesel engine which provides a low fuel economy and which can correspond to the regulation of exhaust emission. The pressure accumulating distribution type fuel injection pump is provided for supplying respective cylinders with fuel that is high-pressured and accumulated in pressure accumulation chambers through a distribution shaft. In the fuel injection pump, function members constituting a high-pressure path, such as a plunger, an injection control valve for fuel injection control, the pressure accumulation chambers, the distribution shaft or the like are arranged in a hydraulic base. One plunger portion is provided for pressure-supplying fuel to the pressure accumulation chambers.
U.S. Pat. No. 5,398,655, which issued to Tuckey on Mar. 21, 1995, describes a manifold referenced returnless fuel system. A fuel pressure regulator for a no-return fuel system for an automotive engine with fuel injectors is disclosed. It has a housing with a flexible diaphragm between first and second chambers. The second chamber has a fuel inlet receiving fuel from a fuel pump with a spring biased valve therein to admit fuel to the second chamber and an outlet to supply fuel to the engine. The second chamber is in continuous communication with the engine to accumulate any fuel expansion that may occur during engine deceleration or when the engine is turned off due to heating of the fuel. The first chamber continuously communicates with the engine air intake manifold so that fuel is supplied to the engine fuel injectors at a substantially constant pressure drop across the injectors. An over-pressure relief by-pass valve responsive to pressure at said fuel inlet will by-pass fuel to a reservoir when pressure in said second chamber opens said spring biased valve. A switch in the by-pass valve acts through a pulse width modulator to reflect the overpressure to the pump drive.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In high Break Mean Effective Pressure (BMEP) fuel injected engines, injectors with very wide dynamic ranges are typically required. These injectors tend to be produced in low volumes and are relatively expensive in comparison to other types of less capable fuel injectors. One way to achieve a larger effective injector dynamic range is to supply a lower fuel pressure at lower engine power operating points and a higher pressure at higher engine power operating points. Another problem that is encountered in the typical constant pressure, mechanically regulated, fuel system is the excessive heat that is transferred to the fuel under low engine power conditions. The traditional system, known to those skilled in the art, employs a pump running at full capacity under all operating conditions. This dictates that under most engine operating conditions a greater than necessary amount of work is done to maintain the target pressure and this excessive work ultimately results in higher fuel temperatures.
It would therefore be significantly beneficial if less work is performed in pumping fuel to a fuel injector under operating conditions that do not require high fuel pressures.